Chapter 1
Introduction
©
National Instruments Corporation
1-3
GPIB-120B User Manual
With the GPIB-120B, it is possible to overcome the following
two configuration restrictions imposed by the ANSI/IEEE Standard
488.1-1987:
•
An electrical loading limit of 15 devices per contiguous bus.
•
A cable length limit of 20 m total per contiguous bus or 2 m times the
number of devices on the bus, whichever is smaller.
With each GPIB-120B, you can add up to 14 additional devices to the bus.
The GPIB-120B appears as a device load on each side of the expansion;
therefore, one GPIB-120B increases the maximum load limit from
15 devices to 28 devices. The cable length limit for the system is also
increased an additional 4 m to 20 m, depending on the number of devices
on that side of the expansion.
All signal expansion is bidirectional, meaning that Controllers, Talkers,
and Listeners can be on either side of the expander. The GPIB-120B
light-emitting diodes (LEDs) indicate the location of the System
Controller, Active Controller, and Source Handshaker, with respect to
the two sides of the expansion.
Because the GPIB-120B is a functionally transparent expander, the same
GPIB communications and control programs that work with an unexpanded
system can work unmodified with an expanded system.
What You Need to Get Started
❑
GPIB-120B
❑
10–18 VDC 9 W power supply
❑
Standard GPIB cables to connect both sides of the GPIB-120B to buses
on either side
